It is known to produce porous ceramics by wet processes such as a foaming method and a method involving the use of heat decomposable beads.
In the foaming method, a foaming agent such as an aqueous solution of hydrogen peroxide is added to a slurry of starting ceramic powder, which is then dried and foamed to make a porous ceramic material. A problem with this method is the difficulty in controlling the pore size and the porosity.
In the other wet process which involves the use of heat decomposable beads, a slurry of a starting ceramic powder is mixed and kneaded with beads of an organic polymer, and after the mixture is shaped, it is heated to burn away the organic polymer and produce a porous ceramic material. This method, however, suffers the disadvantage that the beads do not shrink upon drying so as to develop distortion of the dried product. Further, the use of beads in a large amount leads to some difficulty in the degreasing step (i.e., the step of removing the heat decomposable substance).